Quick answer
You stop a wet room leaking by tanking the whole floor and lower walls, building correct falls to the drain, and sealing every joint and penetration. A leak is almost never the tiles — it’s water finding a gap in the waterproofing underneath. Get the membrane, the falls and the drain right, and a wet room stays dry for decades.
The three things that keep a wet room dry
People assume the tiles and grout are what hold water back. They don’t — grout is porous and tiles have joints. The real barrier sits hidden beneath them. A wet room stays watertight because of three things working together, and a leak means one of them was skipped or rushed.
1 · Full tanking
A continuous waterproof membrane over the entire floor and the lower walls, lapped up the walls and bonded around the drain. This is the actual barrier. More on what tanking is.
2 · Correct falls
The floor is graded so every drop of water runs to the drain rather than pooling. No standing water means nowhere for it to sit and work at a weak point.
3 · A bonded drain
The drain is tied into the tanking with a sealed flange, so water that reaches it goes down the waste — not around the edge of it. This junction is where lazy installs fail.
Where wet rooms actually leak
When we’re called to fix someone else’s leaking wet room, it’s nearly always one of a handful of predictable failures — and every one of them is avoidable:
- No proper tanking — tiled straight onto board, relying on grout. It will fail.
- Membrane not lapped at corners — the floor-to-wall junction is the classic weak spot.
- Drain not bonded to the membrane — water sneaks around the flange and into the floor.
- Wrong or flat falls — water pools, sits, and eventually finds a way through.
- Tanking rushed before it cured — tiled over too soon, so the seal never set properly.
- Flexing floor — an upstairs timber floor that wasn’t reinforced cracks the membrane.
Notice the pattern: none of these are visible once it’s tiled. That’s exactly why you want it done right the first time, by someone who treats tanking as the most important stage — because it is.
By the time the tiles go on, the waterproofing is already done. Get those hidden layers right and the visible finish never has to fight the water.
How we make sure a wet room won’t leak
Our process is built around the waterproofing, not bolted on at the end. We start with a rigid, stable base — reinforcing upstairs timber floors so they can’t flex. We form the falls accurately toward the drain, then apply a full tanking system across the floor and lower walls, paying particular attention to corners, the wall junction and the drain flange. Then — and this is the part people skip — we let it cure properly before a single tile goes on. Only once the membrane has set do we tile, grout and seal.
That discipline is why a properly built wet room is genuinely low-risk. It also means our wet rooms are covered by our workmanship guarantee — see the full process and local examples on our wet room installation hub, and the cost breakdown on our wet room cost page. If you’re still deciding between a fully open wet room and a tray-based option, our wet room vs walk-in shower guide weighs up the waterproofing demands of each.
Common questions
Does grout and sealant stop a wet room leaking?
No — grout is porous and sealant only protects edges. They keep the finish tidy, but the real waterproofing is the tanking membrane underneath. Relying on grout alone is the single most common cause of wet room leaks.
Can a leaking wet room be fixed without ripping it out?
Sometimes a localised failure at the drain or a wall junction can be remedied, but if the tanking is missing or failing across the floor, the only reliable fix is to take it back and tank it properly. We’ll always assess and tell you honestly.
How long does the tanking take to cure?
It depends on the system and conditions, but it needs to be fully set before tiling — usually a day or so within the overall 4–7 day install. We never tile over green tanking; that’s how seals fail.
Dry for the long run
Get a wet room that’s tanked properly
We treat waterproofing as the job, not an afterthought. Tell us about your room and we’ll give you a fixed written quote and a guaranteed, watertight finish.